Guide bars of this kind are used to guide a revolving saw chain. They are secured with one end inside the motor-driven chain saw and from there project freely to the front for their entire length. Because it is attached at one end in this way, the guide bar has to withstand major forces, particularly when it is loaded at its free end as in plunge-cutting work. If the guide bar should catch in the kerf for example, very severe bending and/or torsional strains may be imparted to the guide bar; the longer the guide bar, the greater the effect of the strains will be.
For these reasons, the guide bar must be extremely sturdy in design, which makes it correspondingly heavy; especially with hand-operated motor-driven chain saws, this is highly disadvantageous because it makes them more difficult to manipulate. Attempts have therefore long been made to reduce the relatively great weight of the guide bar.
Initial attempts to reduce the weight included providing openings in the form of penetrations through the flat side of the guide bar; however, this soon proved unsuitable because this considerably lessened the bending strength of the guide bar and made it less resistant to torsion. Thereafter attempts to increase the stability were made by filling the openings of the guide bar, which as a rule was of solid material such as steel, with lighter-weight materials such as light metal. Guide bars of this kind are disclosed, for example, in German Pat. No. 728,639 and Canadian Pat. No. 657,445. Although it was possible with such embodiments to attain a notable weight reduction as compared with solid steel guide bars, these embodiments with lighter-weight metal inserts have not proved satisfactory in practice because they did not provide the required stability.
It is also known for motor-driven chain saw guide bars that are fastened at one end to be made up of several pieces, preferably three, instead of only one piece. Guide bars of this kind are of sandwich construction such that the two outer parts of the guide bar have closed faces, while a spacer plate is placed in the interior between these closed outer faces; the spacer plate is also made of steel but has openings to effect a reduction in weight. These three layers are preferably joined together to form a unit by means of welding.
Although such versions can be much lighter than solid guide bars, they still lack the rigidity of solid guide bars, which must be capable of withstanding maximum loads in long-term use. It has also been found that in multi-layer guide bars, the rigidity of the guide groove is not entirely satisfactory because the groove widens after relatively long use and the reliable guidance of the saw chain that is required is no longer assured. These sandwich-construction guide bars are therefore no longer used where highest loading of the apparatus is expected.